Structural response of thin-walled austenitic pipes to radiolysis gas detonations

Abstract
Radiolysis gas is a mixture of gaseous hydrogen and oxygen, which is generated by dissociation of water under the influence of gamma and neutron radiation. Radiolysis gas aggregations can appear for example in safety-relevant piping of nuclear power plants. The detonation of such gas mixtures can not be excluded in all cases. Within the scope of a research project funded by the German Federal Ministry of Economics and Technology (BMWi), the basis for the assessment of the related risk potential for plant operation shall, among others, be provided. Detonation tests and numerical evaluations are performed to simulate detonations of radiolysis gas in pipes with O.D. x t=(114.30×6.02) mm made of austenitic steel under operating pressure of 70 bar. It is observed, that depending on the ratio of detonating gas to nitrogen rupture of the pipe can occur in different distances from the ignition. Due to the high-rate response of the pipes to the detonations, multiple longitudinal cracks and fragmentation occurred in certain cases. For the numerical investigations an appropriate material constitutive law is chosen in order to describe the material behaviour including strain rate sensitivity and thermal softening at high deformations. Several small-size specimen tests are performed in order to evaluate the required material parameters. For determination of the local strain distribution during the tests appropriate optical measurement is used. The material model is validated by numerical simulations of tensile and compressive tests. The numerical simulation of the deformation behaviour of the pipes fits well into the test results.